To assess the safety of xenotransplantation of NTCELL [immunoprotected (alginate-encapsulated) choroid plexus cells] in patients with Parkinson's disease, assessed over the duration of the study, by monitoring the occurrence of adverse events and serious adverse events, including clinical and laboratory evidence of xenogeneic infection in transplant recipients and their partners/close contacts. Subsequent safety follow-up will include lifelong monitoring for clinical and laboratory evidence of xenogeneic infection.